1. Technical Field
The disclosure generally relates to heat transfer apparatuses, and particularly to a flat heat pipe with high heat transfer performance.
2. Description of Related Art
Heat pipes are widely used in various fields for heat dissipation purposes due to their excellent heat transfer performance. One commonly used heat pipe includes a sealed tube made of heat conductive material, with a working fluid contained therein. The working fluid conveys heat from one end of the tube, typically referred to as an evaporator section, to the other end of the tube, typically referred to as a condenser section. Preferably, a wick structure is provided inside the heat pipe, lining an inner wall of the tube, and drawing the working fluid back to the evaporator section after it condenses at the condenser section.
During operation, the evaporator section of the heat pipe maintains thermal contact with a heat-generating electronic component. The working fluid at the evaporator section absorbs heat generated by the electronic component, and thereby turns to vapor. Due to the difference in vapor pressure between the two sections of the heat pipe, the generated vapor moves, carrying the heat with it, toward the condenser section. At the condenser section, the vapor condenses after transferring the heat to, for example, fins thermally contacting the condenser section. The fins then release the heat into the ambient environment. Due to the difference in capillary pressure which develops in the wick structure between the two sections, the condensate is then drawn back by the wick structure to the evaporator section where it is again available for evaporation.
Wick structures currently available for heat pipes can be fine grooves defined in the inner surface of the tube, screen mesh or fiber inserted into the tube and held against the inner surface of the tube, or sintered powder bonded to the inner surface of the tube by a sintering process. The grooved, screen mesh and fiber wick structures provide a high capillary permeability and a low flow resistance for the working medium, but have a small capillary force to drive condensed working medium from the condenser section toward the evaporator section of the heat pipe. In addition, a maximum heat transfer rate of these wick structures drops significantly after the heat pipe is flattened. The sintered wick structure provides a high capillary force to drive the condensed working medium, and the maximum heat transfer rate does not drop significantly after the heat pipe is flattened. However, the sintered wick structure provides only a low capillary permeability, and has a high flow resistance for the working medium.
What is needed, therefore, is a flat heat pipe which has a high heat transfer performance overall.